In an image forming apparatus such as a laser printer, a processing unit, which includes a casing, a developing roller that is rotatably supported by the casing, and a photosensitive drum which is opposed to the developing roller and on which an electrostatic latent image is formed, is provided. When toner that is carried on the developing roller opposes the electrostatic latent image of the photosensitive drum, a visible image is formed due to the toner being selectively transferred to the electrostatic latent image.
Related-art discloses a developing roller used in such an image forming apparatus. The related-art developing roller is formed by providing an elastic rubber layer around a metal shaft. However, because a metal core cut from steel is used in the metal shaft, there is a problem that the weight of the developing roller increases.
In view of this problem, related-art discloses a developing roller formed by providing a thin elastic rubber layer around a hollow pipe and press fitting a flange having a shaft into both ends of the pipe (JP-A-2000-275955). Thereby, the weight of the developing roller is reduced.
When assembling the related-art developing roller including a hollow pipe to a casing, the flange having a shaft is received by a shaft receiving unit, so as to be supported by the casing. Thus, as there are multiple elements between the hollow pipe and the casing, an axial accuracy of the developing roller to the casing becomes low.
The axial accuracy of the developing roller to the casing can be improved by not attaching the flange to the hollow pipe but supporting an outer circumference of the hollow pipe by a supporting member and attaching a pipe section directly to the casing. However, as there is little difference between an outer diameter of the developing roller including the elastic rubber layer and an outer diameter of the pipe section, when the outer circumference of the pipe section is supported by the supporting member, the supporting member interferes with the photosensitive drum.